In general, composite three-phase ports (represented by the single signal line) can only connect to other composite three-phase ports. However, expanded three-phase ports can connect to other Simscape Power Systems components. There are two options for connecting the three-phase signals in your circuit:
1) Right-click on a block and select Simscape > Block choices > Expanded three-phase ports. Each of these individual ports can then be connected to other Simscape Power Systems components.
2) Three-phase signals can be combined and separated with the "Phase Splitter" component. Therefore, you may combine three separate signals emanating from other Simscape Power System components into a composite three-phase signal with this. More information on this block can be found here:
A further reference on three-phase ports is here:
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